1. Technical Field
This invention relates to sonar systems, and more particularly to sonar systems which use a fixed array of transducers to scan selected angular sectors of a field of view.
2. Description of the Related Art
The conventional method of using a fixed array of transducers to scan selected angular sectors is to employ beamforming circuitry which adjusts the relative phase associated with the signal of each of the transducers to obtain phase coherency for acoustic transmission directed along the selected angular sector. The acoustic field is sampled, for example, by discrete and separated piezoelectric ceramic element sensors that are arranged in some convenient geometry. The outputs of these elements are amplified, filtered, and fed to beamformer circuits which delay or phase-shift the signals from the elements by respective amounts, and combine the delayed or phase-shifted signals to provide the beam output. These circuits are replicated to form outputs for multiple beams. The beamforming circuits may be entirely digital in nature and use multiplier accumulator chips, memory chips, and control chips, or they may be analog and use operational-amplifier circuits or bulk delay lines. In some cases, digital and analog hybrid circuits are used. In other cases, charge transfer devices (CTD) or surface acoustic wave (SAW) devices are used as delay line devices.
In general, the multiple beam beamforming circuits comprise a substantial portion of the space and weight resources allocated to the sonar system. In many cases the sonar system, space and weight limitations are rather severe, and therefore a reduction in the capabilities of other sonar subsystem components is required to accommodate the multiple beam beamforming circuits. In some cases the amount of hardware required for the beamforming process dictates tradeoffs which may adversely affect the overall system performance. The beamforming circuits themselves are rather complex and generally require a significant amount of design time and high construction tolerances for a specific implementation. In short, the multiple beam beamformer circuits make the sonar system larger, heavier, and more complex than a specific application may require.